Why do they do it? As we saw in the study, for mammals, shaking is a really efficient way of drying off, and they can lose up to 70% of the water on their body within seconds. If they were to rely on evaporation, it might take up 20% of their daily food energy to warm themselves up. Little animals have to shake faster to generate the same kind of forces necessary to get water off them – amall mice can generate up to 70G by shaking up to 30x a second. Bears shake at about 4x a second – as they are so large they generate quite big forces straight away, plus loose skin means they can get really good speed and rotation of their fur as they shake… which all adds to the force they can generate.